This invention relates to a display arrangement comprising an electro-optical display medium positioned between two supporting plates, a system of picture elements arranged in rows and columns, each picture element being constituted by two picture electrodes provided on the surfaces of the supporting plates facing each other, a system of row and column electrodes for driving the picture elements, the row electrodes being provided on one supporting plate and the column electrodes being provided on the other supporting plate, and a system of switching elements, at least one first asymmetrical non-linear switching element being arranged between a first row electrode and a column electrode in series with each picture element and at least one additional asymmetrical non-linear switching element being arranged in series with the first asymmetrical non-linear switching element between the first row electrode and a second row electrode. The additional switching element is connected in the same direction as the first asymmetrical non-linear switching element between the picture element and the second row electrode.
It should be noted that in the present Application the terms "row electrode" and "column electrode" may be interchanged so that, where a row electrode is concerned, also a column electrode may be meant while simultaneously changing column electrode into row electrode. The term "asymmetrical" non-linear switching element" is to be understood to mean in this Application, in the first instance a diode usual in the technology for manufacturing the said display arrangements, such as, for example, a pn diode, a Schottky diode or a PIN diode made of monocrystalline, polycrystalline or amorphous silicon, CdSe or other semiconductor materials, although other types of non-linear switching elements, such as, for example, bipolar transistors with a shortcircuited base-collector junction or MOS transistors whose gate is connected to the drain zone, are not excluded.
Such a display arrangement is suitable for displaying alpha-numeric video information by means of passive electro-optical display media, such as liquid crystals, electrophoretic suspensions and electrochrome materials.
The known passive electrooptical display media generally have an insufficiently steep threshold with respect to the applied voltage and/or have an insufficient intrinsic memory. In multiplexed matrix display arrangements, these properties result in that, in order to obtain a sufficient contrast, the number of lines to be driven is limited. Due to the lack of memory, the information supplied to a selected row electrode via the column electrode has to be written again and again. Moreover, the voltages supplied at the column electrodes are applied not only across the picture elements of a driven row electrode, but also across the picture elements of all the other rows. Thus, for the time in which they are not driven, the picture elements are subjected to an effective voltage which must be sufficiently small so as not to bring a picture element into the ON state. Furthermore, with an increasing number of row electrodes, the ratio of the effective voltage to which a picture element is subjected in the ON and OFF state, respectively, decreases. Due to an insufficiently steep threshold, the contrast between picture elements in the ON and OFF state then decreases.
It is known that the number of rows to be driven can be increased by providing, per picture element, an additional switching element. This switching element ensures that a sufficiently steep threshold is obtained with respect to the applied voltage and ensures that the information supplied to a driven row electrode is maintained across a picture element for the time in which the remaining row electrodes are driven. The switching element also prevents a picture element from being subjected to an effective voltage meant for other picture elements in the same column for the time in which it is not driven.
A display arrangement of the kind mentioned in the opening paragraph is described in the article "Liquid Crystal Matrix Displays" by B. J. Lechner et al, published in Proc. I.E.E.E., Vol. 59, No. 11, November 1971, p. 1566-1579, more particularly p. 1574.
The arrangement shown therein and the associated method of driving, designated as the ac-D.sup.2 C method, have the advantage that by means of unilateral non-linear switching elements (diodes), nevertheless an alternating voltage is obtained across the picture elements. However, this is at the expense of a second row electrode, to which the desired voltages are supplied by means of additional circuits.